This application will focus on the methodological development and therapeutic applications of proteins with unusual architectures. Selected proteins for our design will be circularized and branch proteins. Target circularized proteins include interleukin-l receptor antagonist which is currently in clinical trials as a drug to reduce severity of sepsis and arthritis; monitor peptide which is a cholecystokinin-releasing factor and may be useful for treatment of digestive disorders; and defensin which is a broad-spectrum antibiotic with promising activity against AIDS-related pathogens. Target branch proteins will include a malaria vaccine containing the protective antigen derived from merozoite surface protein (MSP-1). This antigen is the most promising vaccine candidate to date. The branch design will incorporate multimeric copies of MSP-1 antigen in a small peptidyl core matrix as multiple antigen peptides (MAPs). The antigen derived from MSP-1 is conformation-dependent and contains multiple disulfide bonds. Together with a T-helper epitope and a built-in adjuvant assembled to form MAPs, it will provide a complete vaccine with an unambiguous structure. This malaria vaccine will be tested for protection against infection challenge in the mouse model by Dr. Carol Long who is a leading expert in malaria. A version of MAPs containing a HIV-1 antigen is currently in Phase I clinical trials as a candidate AIDS vaccine. The unifying theme of this application is the development and application of the domain ligation strategy recently conceptualized in our laboratory. It is a method to link or circularize totally unprotected peptide and protein segments via a peptide bond without activation. This method is well suited for the synthesis of circularized and branch proteins which are inaccessible directly by the recombination DNA method and are difficult to obtain by the conventional peptide synthesis approaches. The domain ligation strategy is a combined approach of organic and peptide chemistry in engineering proteins for therapeutic applications.